1. Field of the Invention
The present invention relates to an inflator for an air bag which is used in an air bag system mounted on a vehicle to discharge a gas for inflating an air bag at the time of collision, and in particular to an inflator for an air bag preferably used in a curtain air bag system which inflates an air bag to cover an approximately entire surface of a side window mainly at the time of side collision in a vehicle.
2. Description of Related Art
In order to protect a passenger from an impact at the time of a vehicle collision, various air bag systems (inflating-type safety apparatuses) are mounted in a vehicle. These air bag systems are formed such that they can achieve an optimal passenger protection according to a seat position of the passenger inside the vehicle, a protecting (restraining) method for the passenger subjected to the impact or the like. Various air bag systems such as one arranged at a driver side, one arranged at a front passenger side, one for protecting a passenger from a side collision, and one for inflating a curtain air bag are provided currently.
These air bag systems of various kinds include an inflator for generating gas for inflating an air bag (a bag body) at the time of activation, and such an inflator is provided, such that a pressurized medium such as a pressurized gas is charged as a gas source for inflating the air bag.
In particular, an air bag system for inflating a curtain air bag (hereinafter, referred to as a “curtain air bag system”) is for inflating and developing a curtain-like air bag over a window of a vehicle instantaneously when the vehicle receives an impact from a lateral direction, and it is for protecting the head or neck of a passenger from the impact at the time of collision or it aims to prevent the passenger from being thrown out of the vehicle at overturn of vehicle. In particular, the curtain air bag system which aims to protect the passenger at the time of overturn of vehicle is required to protect the passenger while the vehicle is turning laterally, and it is necessary to maintain a developing state of the bag for at least five seconds. For this reason, in an inflator used in the curtain air bag system, a medium whose volume change due to cooling is small, for example, a pressurized gas such as helium is used as a gas source for inflating the air bag. This kind of pressurized gas is charged in a housing which is generally a pressure-resistance container and it is prevented from flowing out of the housing by being sealed with a rupturable plate or the like. And such a mechanism is employed that the rupturable plate is ruptured by an igniter or the like to feed the pressurized gas into a curtain air bag (a bag body) at the time of activation.
In such an inflator, since discharging of the pressurized gas is conducted by rupturing of the rupturable plate, fragments of the ruptured rupturable plate may be mixed in a gas flowing into the air bag unless any countermeasure is taken. Since such fragments are not preferable in view of safety at activation of the air bag system, these fragments should be blocked from flowing into the air bag.
In order to block inflow of the fragments into the air bag, a filter or the like can be disposed in the inflator to arrest the fragments. However, the filter or the like needs to be disposed in a gas flow passage, and operation performance, in particular, the amount of the discharged gas may be changed at activation due to change of a ventilation resistance caused by the clogging with arrested fragments. Accordingly, unless an output change of an inflator due to clogging in the filter is considered in advance, a sufficient operation performance can not obtained, or even if the output change is considered in advance, the operation performance is eventually controlled by an uncertain factor such as a ruptured state of the rupturable plate.
Therefore, it is conventionally desired to provide an inflator for an air bag which prevents fragments of the rupturable plate from flowing into an air bag and shows a stable operation performance.
Further, the air bag system is desired to have a smaller volume in order to obtain occupants' space inside a vehicle or the like, and particularly in the curtain air bag system, its installation place is limited to a place near a window on a side surface of the vehicle because of its purpose of installation, and thereby, an inflator used in the system desirably has a smallest volume and is elongated axially.
Especially, when curtain air bags are inflated, it is necessary to equally develop a curtain air bag for a front seat and a curtain air bag for a rear seat, and it is desired to arrange an inflator for a curtain air bag at a substantially middle portion between the front seat and the rear seat, having the same distance to both curtain air bags in order to equally develop the curtain air bags in the both seats. However, a mounting space for the inflator in the vicinity of a side window is limited, and therefore, the inflator is obligated to be arranged only in either side of the front seat and the rear seat. As a result, there is such an actual situation that it becomes difficult to develop the front and rear curtain air bags at the same time. For example, if an inflator is mounted in the vicinity of an A pillar (the forefront pillar of the vehicle) of the vehicle to develop the front and rear curtain air bags, the curtain air bag in the rear seat side is always delayed starting and completing development because an inflating gas has to move a longer distance (a distance to the air bag) to reach the air bag in the rear seat side. On the contrary, when the inflator is mounted in the vicinity of a C pillar (the rearmost pillar of the vehicle), the curtain air bag in the front seat side is delayed completing development.
Further, in inflators used in various kinds of air bag systems, it is also important that manufacturing cost can be reduced, a sufficient durability can be ensured and further a rapid operation can be made as required, and such an object completely applies to the inflator used in the curtain air bag (hereinafter, referred to as an “inflator for a curtain air bag). Here, it is expected that an inflator is made of iron in order to reduce manufacturing cost, but a vehicle mounted with the inflator is used in various environments including an extreme cold place and a tropical area, and in such a case that the inflator is used in an area having a large difference in temperature throughout a day, water drops adhere to an inflator surface for a long time, which causes rust. And if rust occur on the inflator surface, there is a risk that the rust influences another part such as an electric circuit or the like positioned in the vicinity of the rust.
Therefore, it is conventionally desired to provide an inflator which can develop a curtain air bag for a front seat and a curtain air bag for a rear seat evenly in addition of a shape limitation of an inflator because of an arrangement place, or an inflator which can solve the problem regarding corrosion effectively.
As the conventional art regarding the curtain air bag system, for example, there is JP-A 9-254736.